12 V-to-1.5 V Switched Capacitor dc-dc Converter in a Submicron CMOS Technology
Vincent Wai-Shan Ng, Seth R. Sanders and Michael Douglas Seeman
This research explores the design and development of CMOS-based switched capacitor (SC) dc-dc conversion circuitry aimed at applications traditionally addressed with the ubiquitous buck converter. The traditional buck converter requires at least one substantial inductor and transistors with voltage rating matched to the input source voltage, which may be costly to integrate in a submicron CMOS technology. The traditional buck converter also suffers from low efficiency or poor power device utilization when used in a high-conversion-ratio application. Further, buck converter efficiency degrades rapidly in low-power modes unless additional special modes (like PFM) are enabled. SC dc-dc converters, on the other hand, can sustain high efficiency with a high conversion ratio, and also over a very wide load range. Moreover, SC dc-dc converters do not require any magnetic or high voltage transistors; each power transistor needs to only block a fraction of the input voltage, thus allowing a high voltage dc-dc converter to be built in a submicron technology with native transistors. To prove our concept, we built a 12 V-to-1.5 V SC dc-dc converter in a 0.18 µm CMOS technology with a peak output current of 1.5 A and a peak efficiency of 98%. This converter is ideal for the point-of-load application in which a dc-dc converter is placed close to an associated load.
Figure 1: Efficiency versus output load condition